Nanobiotechnology, a new field of technology that unites nanotechnology and biotechnology, has been created and been developing rapidly. The nanobiotechnology is highly expected since it contributes to production of bioelectronics element and biosensor, and to development of bio-chip for DNA and protein, for example.
As described above, bioelectronics element and biosensor technique are extremely important in the nanobiotechnology. DNA chips and protein chips are highly expected. For these chips, a sensor need be produced and controlled in consideration of molecular size, because the chips should sense a single molecule such as DNA and protein. Therefore, development of a biosensor by using semiconductor processing technique has been started.
Specifically, for example, such a biosensor is now under development that an antibody for a virus to be detected is immobilized on a silicon nanowire and that can detect the a virus electrically when even one virus attaches to the antibody.
As described above, in order to further facilitate the development of biosensors using semiconductor processing technique, it is considered essential to develop techniques of placing and immobilizing a desired protein easily and accurately onto a substrate (supporter), such as silicon or glass.
There has been some methods for binding and immobilizing protein on a surface of glass; (1) binding by physical adsorption, (2) immobilizing the protein by using a cross linker which make the protein covalently bind to a surface of a carrier on the glass surface modified with a silane coupling agent or the like.
Method (1) is a method in which the binding is carried out by utilizing electric charge and/or hydrophobicity of the protein. This method (1), however, can not be the one which adsorbs a desired protein, because intensity of binding varies depending on proteins. Also, even if the protein is bound to the glass surface, there is a possibility that the protein molecules are bound at various sites to the glass surface. This often makes differences in protein activity.
Method (2) enables immobilization of a desired protein to the glass surface. However method (2) also causes modification at various sites of protein molecules, thereby affecting protein activity. There has been a study on modification agents generating orientation. However, it is inevitable that operation in modifying substrate surface and cross-linking proteins becomes complicated.
As a method to solve the problems described above, a method has been reported, in which a desired protein is presented on a glass surface which is modified with polyethylene containing copper ion, the protein being bound with a tag which recognizes copper ion. (See Non-Patent Citation 1)
Additionally, it has been reported that a protein to which 9 arginine residues (polyarginine tag) are added can be adsorbed directly to a glass surface and silica resin, without deteriorating its enzyme activity. (See Non-Patent Citation 2)
[Non-Patent Citation 1]
    Enzymatic activity on a chip: The critical role of protein orientation, T. Cha, A. Guo, X.-Y., Zhu, Proteomics, 5, 416-419 (2005).[Non-Patent Citation 2]    Fuchs, S. M. & Raines, R. T. Polyarginine as a multifunctional fusion tag. Protein. Sci. 14, 1538-1544 (2005).